The present invention relates to a method for the manufacturing of a drill bit for percussive rock drilling, as well as to a rock drill bit and a button for use in percussion drilling operations.
A rock drill bit is intended to crush rocks. This is achieved by generating impacts or shock waves in a drilling machine and transferring those via a rod to the end where the drill bit is secured. The crushing is achieved by so called buttons or chisels of hard metal, which are positioned in the front surface of the steel drill body. The buttons and the chisels are subjected to high strains during impacting. Today the buttons or the chisels are secured by being pressed into drilled holes or by being soldered in milled grooves. In drilled holes, buttons are held by friction to the bore wall or, in case of chisel bits, with the assistance of brazing material. During brazing, a material often is applied having relatively low strength and which melts at low temperature, which limits the strength of the joint.
The bending moment on a button must be resisted by the bore hole in the drill body, so relatively deep holes are required in the drill body. By xe2x80x9cdeepxe2x80x9d is meant holes in the magnitude of 5-20 mm, depending of the dimensions of the hard metal. Due to the deepness of the holes, the geometry of the drill body must be oversized. Since the volume of the drill body is limited, also the number of buttons and their possible positions become limited. Thereby the options for positioning of flush channels for flushing fluid in the drill body become limited. In addition, only a smaller part of the hard metal of the button is used for machining. In case the buttons are diamond coated, the heat from brazing can damage the diamond layer.
One object of the present invention is to provide a method for the manufacturing of drill bits for percussive rock drilling, and to provide a rock drill bit and a button, which counteract the above-captioned drawbacks.
Another object of the present invention is to provide a rock drill bit, which allows great versatility regarding the creation of cavities in the drill body.
Still another object of the present invention is to provide a button, which enables a simple mounting to the drill body.
Still another object of the present invention is to provide a method for the manufacturing of drill bits for percussive rock drilling, which is fast and efficient.
One aspect of the present invention relates to a rock drill bit for percussive drilling which comprises a bit body having a working end formed by a forward surface and a surrounding peripheral surface. Peripheral buttons are arranged in the peripheral surface in the form of a peripheral wreath of peripheral buttons. Front buttons are arranged in the forward surface inside of the wreath of peripheral buttons. At least one of the front buttons is welded to a substantially flat portion of the forward surface. The at least one button has a protruding portion which protrudes from the forward surface. The protruding portion has a diameter D and a height H, wherein H/D less than 1.2. The at least one button is metallurgically bound to the forward surface.
Another aspect of the invention relates to a method of manufacturing a rock drill bit for percussive drilling. The bit comprises a body having a head portion on which a working end of the button is disposed. The working end comprises a forward surface and a surrounding peripheral surface. Peripheral buttons are arranged in the peripheral surface to form a wreath of peripheral buttons. Front buttons are arranged in the forward surface. Each peripheral and front button includes a protruding portion protruding forwardly from the working end. The protruding portion has a maximum diameter D and a height H. The method comprises the steps of:
A) providing a source of current having two electric poles,
B) connecting one of the poles to the bit body and the other pole to at least one of the buttons having a ratio of H/D less than 1.2,
C) converging the forward surface and the at least one button such that an electric arc is formed between the forward surface and the button, the electric arc melting opposing faces of the forward surface and the button,
D) pressing the button against the forward surface,
E) allowing the opposing faces to solidify, and
F) repeating steps A-E for other buttons of the bed having a ratio H/D less than 1.2.